Publications

Dille, A.,  Kervyn, F.,  Bamulezi Ganza, G.,  Mawe Ilombe, G.,  Buzera Kalikone, C.,  Mugaruka Bibentyo, T.,  Safari Makito, E.,  Monsieurs, E.,  Delvaux, D.,  Smets, B.,  Kervyn, M. & Dewitte, O. 2018. ‘Characterising drivers and mechanisms of landsliding in a tropical context – Ikoma landslide, DR Congo’. Geologica Belgica. Book of abstracts. Leuven.

Résumé de colloque

Understanding slope evolution and their related hazards relies on accurate landslide process characterisation. This ideally needs knowledge on the timing of slope deformation phases as it allows to understand the link between slope instability and environmental drivers such as seismicity and climate for instance. However, for many regions, especially in tropical environments where vegetation growth can be very quick and low-capacity data collection policy is commonplace, such information remains rare. Here we focus on a large deep-seated landslide in the landslide-prone and data-scarce Kivu rift, in eastern DR Congo. This landslide, developed in (weathered) basalt and regolith, is known for having undergone large deformations during the recent years. The location of this landslide in a seismically active tropical context, as well as the presence of recent and highly apparent deformation features at its surface make it a perfect natural laboratory to study landslide processes. Using high-resolution topography and orthomosaic obtained from Unmanned Aerial Vehicle (UAV) and Structure from Motion (SfM) photogrammetry in addition to detailed field investigations and satellite imagery allows the identification of three different landslide kinematic units that show contrasting movement styles. The presence of these different sectors highlights interactions within the landslide body (e.g. destabilisation due to material accumulation or support removal) but also the occurrence of multiple deformation episodes. The study of the evolution of the slope stability over the past two decades supports the interpretation of the landslide mechanisms. By confronting rainfall time series and major earthquake sequences to the slope evolution, we also show that the relation between instability triggers and slope deformations is not straightforward; e.g. the largest instability occurred at the end of a dry season during a period of relatively low seismicity. Instead of direct influence of external triggers, we show that some phases of instability (and related slope failures) may ultimately be caused by the intrinsic evolution of the hillslope associated with strength degradation of the slope material through time. Our results question the relative weight of the commonly recognized causes and drivers of slope instability, highlighting the relevance of considering interactions between dynamic earth processes, as well as the likely particularity of landslide processes in such tropical environment. The analysis of the landslide processes provided here will help in the evaluation of the landslide hazard in the particular data-scarce Kivu Rift, but also across other regions of subtropical Africa and elsewhere where similar environmental conditions are met.